I. Field of the Invention
The present invention relates generally to the fields of biology and medicine. More particularly, it concerns compounds and methods for the treatment and prevention of diseases such as those associated with oxidative stress and inflammation.
II. Description of Related Art
The IκB kinases, IKKα and IKKβ, are related kinases that play a major role in the activation and regulation of the transcription factor, NF-κB. They are induced by stimuli such as TNFα and IL-1 to phosphorylate residue Ser32 and Ser36 of IκBα, the regulatory subunit of NF-κB. The IκB kinase (IKK) complex comprises three proteins: the catalytic subunits, IKKα and IKKβ, and the regulatory subunit, IKKγ (NEMO). Without being bound by any particular mechanism or theory, the phosphorylation of IκBα results in ubiquitination and subsequent degradation in the proteasome. This releases NF-κB dimers from the cytoplastic NF-κB-IκB complex, allowing NF-κB to translocate to the nucleus where it regulates the transcription of numerous target genes. IKKβ appears to be the principal kinase, whereas IKKα is not required for activation of IKK and degradation of IκBα by proinflammatory stimuli. IKKβ triggers the activation of NF-κB in response to infectious agents and proinflammatory cytokines, making it an attractive drug target for the treatment of inflammatory diseases. In addition, NF-κB is over-expressed or constitutively activated in many cancer cells where it induces the expression of anti-apototic genes and/or suppression of pro-apototic genes. A number of anticancer agents can also induce the activation of NF-κB, which may culminate in the ability of the malignant cell to become drug resistant. Thus, the development of IKKβ inhibitors represents potential therapeutics for the treatment of both cancer and inflammation (Karin et al., 2004).
The anti-inflammatory and anti-proliferative activity of the naturally occurring triterpenoid, oleanolic acid, has been improved by chemical modifications. For example, 2-cyano-3,12-diooxooleana-1,9(11)-dien-28-oic acid (CDDO) and related compounds have been developed (Honda et al., 1997; Honda et al., 1998; Honda et al., 1999; Honda et al., 2000; Honda et al., 2000; Honda, et al., 2002; Suh et al. 1998; Suh et al., 1999; Place et al., 2003; Liby et al., 2005). The methyl ester, CDDO-Me, is currently being evaluated in phase II clinical trials for the treatment of melanoma, pancreatic cancer, diabetic nephropathy and chronic kidney disease.
Three-ringed compounds, whose rings A and C have enone functionalities similar to those of CDDO, have been shown to be a novel class of potent anti-inflammatory, cytoprotective, growth suppressive, and proapoptotic compounds (Favaloro et al., 2002; Honda et al., 2003; Honda et al., 2007). Among these compounds, TBE-31 was found to inhibit nitric oxide (NO) production at low nanomolecular concentrations in RAW cells stimulated by interferon-γ (iNOS assay). Notably, orally active TBE-31 is exceptionally potent against aflatoxin-induced liver cancer in rats (Liby et al., 2008). Furthermore, in vitro and in vivo potencies of TBE-31 are much higher than those of CDDO.

Both CDDO and TBE-31 are multifunctional agents, which regulate proteins involved in inflammation, oxidative stress, differentiation, apoptosis, and proliferation. Without being bound by any particular mechanism or theory, these proteins, including, e.g., IKKβ, Keap1, and JAK1, are regulated by CDDO and TBE-31 by reversible and selective Michael addition between their cyanoenone functionality and the SH groups of cysteine residues on these proteins (Scheme 1); Couch et al., 2005; Dinkova-Kostova et al., 2005). For example, Cys179 on IKKβ was identified as one of targets of CDDO-Me (Ahmad et al., 2006). By binding to this site, CDDO-Me blocks the binding of NF-κB to DNA and thus inhibits transcriptional activation. It has also been reported that CDDO-Me inhibits the JAK1→STAT3 pathway by directly binding to JAK1 at Cys1077 and STAT3 at Cys259 (Ahmad et al., 2008). The small molecule inhibitors of the STAT3 pathway are effective as anticancer agents in vitro and in animal models.

Synthetic triterpenoid analogs of oleanolic acid have also been shown to be inhibitors of cellular inflammatory processes, such as the induction by IFN-γ of inducible nitric oxide synthase (iNOS) and of COX-2 in mouse macrophages. See Honda et al. (2000a); Honda et al. (2000b), and Honda et al. (2002), which are all incorporated herein by reference. For example, one of these, 2-cyano-3,12-dioxooleane-1,9(11)-dien-28-oic acid methyl ester (CDDO-Me), is currently in clinical trials for a variety of disorders related to inflammation, including cancer and diabetic nephropathy. Synthetic derivatives of another triterpenoid, betulinic acid, have also been shown to inhibit cellular inflammatory processes, although these compounds have been less extensively characterized (Honda et al., 2006). The pharmacology of these synthetic triterpenoid molecules is complex. Compounds derived from oleanolic acid have been shown to affect the function of multiple protein targets and thereby modulate the activity of several important cellular signaling pathways related to oxidative stress, cell cycle control, and inflammation (e.g., Dinkova-Kostova et al., 2005; Ahmad et al., 2006; Ahmad et al., 2008; Liby et al., 2007a). Derivatives of betulinic acid, though they have shown comparable anti-inflammatory properties, also appear to have significant differences in their pharmacology compared to OA-derived compounds (Liby et al., 2007b). Further, it is not certain that the triterpenoid starting materials employed to date have optimal properties compared to other possible starting materials. Given that the biological activity profiles of known triterpenoid derivatives vary, and in view of the wide variety of diseases that may be treated or prevented with compounds having potent antioxidant and anti-inflammatory effects, and the high degree of unmet medical need represented within this variety of diseases, it is desirable to synthesize new compounds with diverse structures that may have improved biological activity profiles for the treatment of one or more indications.